The present invention relates to a one-part type anaerobically curable composition which exhibits good storage stability and gives a cured resin having excellent elasticity and is environmentally safe since it does not require any irritating organic peroxide to provide a cured product, as well as a process for preparing such a curable composition.
There have been known a lot of anaerobically curable compositions which are liquid in air but bring about polymerization reaction upon isolating them from air and are cured to exhibit adhesive action. Utilizing such characteristics, these compositions are used in locking of bolts and nuts, fixing of bearings or shafts of motors, filling and repairing of pinholes in castings and the like instead of conventional mechanical means, to increase production efficiency and to save labor. Those compositions are composed of polymerizable monomers an organic peroxide, a curing accelerator and a gelling stabilizer, and are made up to balance the amounts of the accelerator and the stabilizer so that they can cure in a short time at room temperature in the form of a one-part composition. So, they do not require the troublesome steps such as mixing two liquid components, pretreatment by curing accelerator and heating in the working operation, but can be bonded by simply filling them into a gap between metal materials. Thus, they can be said to be a very efficient adhesive. However, because the polymerizable monomer to be used is normally a polymethacrylate having a low molecular weight, the resulting cured resin has the defect in that it has poor elasticity although it is solid and tough. Thus, such a composition was difficult to apply to parts where there was a large change in temperature or where resistance to bending was required. Also, there have been problems with respect to bad odors and skin-irritating properties, because a considerable amount of organic peroxides are used therein as a curing agent.
To provide anaerobically curable compositions which cure to resilient resins, it has been proposed to dissolve solid rubbers in such compositions as shown in Japanese Patent Publication Nos. 25938/75 and 28177/79 as well as Japanese Laid-open Patents Nos. 4243/76 and 65065/81 and the like. In order to provide cured products with resilient properties, however, it is necessary to dissolve a considerably large amount of rubbers therein. When such a large amount of rubber is used, the resulting composition itself may be solid instead of liquid. Moreover, the rubber itself has a poor or no polymerizable property, and thus the resulting composition results inevitably in an adhesive having a slow adhesion speed.
On the other hand, the conventional anaerobically curable compositions often use an organic peroxide as a curing agent. Such organic peroxides, however, have defects in that they have bad odors, and sometimes irritate human skin.
The salt of o-benzoic sulfimide with an amine represented by the general formula, ##STR1## (wherein R.sub.1 and R.sub.2 are hydrogen or methyl group, respectively) is disclosed in Japanese Patent Publication Nos. 39480/78, 47266/78, 28176/79 and 1958/80 Specifications. This salt acts as an effective curing agent or accelerator for the composition of the present invention. The compound, o-benzoic sulfimide, which is one component of the salt used as a curing agent, is better known by the name, saccharin.